1. Field of the Invention
The present invention relates to improvements in a hydraulic shock absorber for vehicles wherein a piston reciprocates in a cylinder to generate an oil pressure attenuating force and absorb shocks.
More particularly, the invention relates to a hydraulic shock absorber for vehicles wherein an elastic body tightening the outer periphery of a piston rod is provided in a piston rod guide part so that the outer periphery of the rod is supported by this elastic body so as to float. Also, the noises at the time of the shock absorbing operation, particularly the shock noises generated by an increase in the hydraulic pressure, and the friction noises of the rod and rod guide part and the vibration and shock noises, are reduced to be as low as possible. The operation is quiet, and the vibrations and noises are few.
2. Description of the Prior Art
There is known a hydraulic shock absorber for vehicles wherein oil is put in a cylinder, a piston is slidably fitted in this cylinder, the cylinder is secured to the wheel, and the piston is secured to the vehicle body so that the shock received by the wheel is absorbed by the hydraulic shock absorbing action between the wheel and the vehicle body.
In this kind of shock absorber, for example, a shock absorber of a McPherson type is formed as follows. The shock absorber is utilized as a part of a suspending link, the lower part of the cylinder is fitted to the wheel, and the upper end of the piston rod is fitted to the body so that the shock absorber is arranged on an incline. Because the shock absorber is provided diagonally, with the upper end of the piston rod directed inwardly and with the lower part of the cylinder directed outwardly, and is used as a suspending link, not only the load in the vertical direction, i.e., the reciprocating direction of the piston, but also the side force will act on the cylinder. As a result, a bending force will act on the piston rod.
In such a shock absorber, the piston rod is supported at its lower end by the sliding surface of the cylinder with the piston, and at its upper end by a rod guide. The rod guide functions as a bearing for the rod. Therefore, the bearing, such as of a synthetic resin, is provided on the inner periphery of the rod guide to guarantee smooth sliding of the rod.
Generally, a slight clearance is formed between the inner periphery of this rod guide and the outer periphery of the rod. This clearance is necessarily formed due to the problem of precision in manufacture, and the fluctuation of the products. But, on the other hand, if the precision is increased and the clearance between the inner periphery of the rod guide and the outer periphery of the rod is made very slight, the friction between them will increase. Thus, the smooth sliding of the rod and the shock absorbing performance will be impeded.
Therefore, in this kind of shock absorber, it is desirable to form a slight clearance between the piston rod and the rod guide of the cylinder, and some clearance is even necessary for the smooth reciprocation to properly perform the shock absorbing function.
However, in such shock absorbers, the presence of a clearance between the piston rod and rod guide produces the following problems.
The noise of the shocks of the internal hydraulic pressure and shocks by the frictional vibrations at the time of the shock absorbing operation will pass out through such a clearance. By the action of the side force, the piston rod will be bent and will contact the guide to generate vibration that will be transmitted to the vehicle body. Therefore, as a measure of preventing noises and vibrations, an improvement to avoid such problems is greatly desired.